In apparatuses that display color images such as a printer and a projection television, light sources for three colors R (red), G (green), and B (blue) are required as light sources. In recent years, as these light sources, a wavelength conversion laser device (a laser oscillator) that converts, with a laser beam in a 900 nm band, a 1 μm band, or 1.3 μm band set as a fundamental wave laser beam, the fundamental wave laser beam into a second harmonic using a nonlinear material (SHG, Second Harmonic Generation) is developed. To realize high conversion efficiency from the fundamental wave laser beam into a second harmonic laser beam in the SHG, it is requested to increase the power density of the fundamental wave laser beam on the nonlinear material and to convert the fundamental wave laser beam into a high-luminance laser beam with less wavefront aberration.
A two-dimensional waveguide laser can realize the high conversion efficiency from the fundamental wave laser beam into the second harmonic laser beam because the two-dimensional waveguide laser can increase the power density of the fundamental wave laser beam. However, an increase in power is restricted because the two-dimensional waveguide laser has a breakage limit due to the high power density. Further, the increase in power is restricted because the power of LD (Laser Diode) beams having a high beam quality in a two-dimensional direction (in the same plane as the two-dimensional waveguide) connectable to the two-dimensional waveguide is generally low.
Therefore, a plane waveguide laser having a one-dimensional waveguide may be used to increase the power of the second harmonic laser beam. In this plane waveguide laser, the increase in power is realized by causing a laser beam to oscillate in a direction perpendicular to a laser beam axis in a flat surface (a direction perpendicular to principal planes of a flat plate) according to a space mode, increasing a beam diameter of the laser beam in the direction perpendicular to the laser beam axis, and changing the laser beam to multiple beams. In such a plane waveguide laser having the one-dimensional waveguide, LD beams as excitation sources only have to be coupled in a one-dimensional direction in the plane waveguide. Therefore, a high-power broad area LD can be used for the plane waveguide laser having the one-dimensional waveguide. As a result, a high-power laser beam can be obtained. Further, a multi-emitter LD in which light emitting points of LD beams are arranged in the one-dimensional direction can be used for the plane waveguide laser having the one-dimensional waveguide. Therefore, laser power larger than that obtained by using the broad area LD can be obtained (see Non-Patent Document 1).    Non-Patent Document 1: IEEE. J. Quantum Electronics Vol. 39 (2003), 495